Various types of self-powered faulted circuit indicators (“FCIs”) have been constructed for detecting electrical faults in power distribution systems, including clamp-on type faulted circuit indicators and test-point type FCIs. Clamp-on type FCIs clamp directly over cables in the systems and may derive their operating power from inductive and/or capacitive coupling to the monitored conductor. Test-point type FCIs are mounted over test-points on cables or associated connectors of the systems and may derive their operating power from capacitive coupling to the monitored conductor. Other prior art FCIs may be either of the manually resetting type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current.
Detection of fault currents in a monitored conductor by an FCI is typically accomplished by magnetic switch means, such as a magnetic reed switch, in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit that produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position, or the FCI may be manually reset. In addition, some prior art FCIs have distinguished between the display of temporary faults and permanent faults. For example, the Schweitzer Engineering Laboratories Model AR-OH (“AutoRANGER”) uses two downward facing red light-emitting diodes (LEDs) to indicate a permanent fault, and a single yellow LED to indicate a temporary fault.
Various prior art FCIs have utilized LEDs to display the presence of a permanent fault or that a temporary fault has occurred on the monitored conductor. For FCIs that are battery-powered, the lifetime of the FCI is a function of the number of faults, the characteristics of the fault display, and other various operating parameters specific to the type of FCI including the percent of time spent installed at different ambient temperatures. An expected lifetime of the FCI can be calculated using an estimation of the expected number of faults, the power use for displaying each fault, temperature, and the estimated background power usage.
The calculated lifetime of an FCI may be used in several ways to assist with ensuring that functioning FCIs are always installed on monitored conductors. In one example, the utility that manages the conductors and FCIs may simply replace all FCIs before the calculated lifetime of the FCI has lapsed. This technique has a disadvantage in that if the number of faults actually experienced was greater than expected, the FCIs may have stopped functioning due to a discharged battery before they were replaced. Further, if the number of faults actually experienced was less than expected, then the batteries in the FCIs would not be fully discharged when the FCIs are removed and disposed. It has been alleged that disposing of batteries with remaining charge is harmful to the environment, and may even be illegal.
Another method is for the FCI to be programmed to flash an indication that the battery life is nearing its end during the last six months of battery life. This method has several disadvantages. For example, in some cases the utility monitoring the conductor and associated FCIs will only survey the FCIs every three years. It would be unlikely, then, that the six-month display indicating an end of battery life would be noticed if the FCIs are only surveyed once every three years, and the FCIs with little or no useful life remaining would not be replaced. Further, it is most likely that the FCI will be noticed during or following a fault (when the FCI should be indicating that a fault is present). If the FCI displays only that the battery is nearing the end of its life, then it is not useful as a faulted circuit indicator. Alternatively, if the FCI displays only that a fault has occurred, then it is not useful to communicate that it is nearing the end of its life. In either case, the conductor is left unmonitored by FCIs. Further still, the indication while displaying low battery indication, quickly depletes battery capacity. Thus, the six-month display shortens the useful life of the FCI.
As is noted above, it is most likely that an FCI will be noticed by a utility when it is indicating the presence of a permanent or temporary fault on the conductor. That is, when utility personnel are using the FCIs to locate a fault on the conductor.